The cord you have linked from Amazon has the wrong sized connector. I wonder if that played a part in this? Intermittent connection could cause a 12v to? 0 to 12v jump anytime the cord is moved...
On Fri, Aug 11, 2023 at 5:46?AM John Z <jdzbrozek@...> wrote:
Ouch, Dave! Yup, a direct hit...
That is a valuable learning experience for all of us.
You mentioned the PD negotiation protocol. No such thing is in QMX!? Maybe it should be in future products from QRP Labs?
USB PD batteries, bricks, etc. are becoming ubiquitous and could be an excellent addition to the QRPer's?toolkit.
JZ KJ4A
On Fri, Aug 11, 2023 at 5:08?AM david mugridge <dave@...> wrote:
My QMX released the magic smoke yesterday and I quickly traced the smoke to a crater in D108, the 5.6V zener on the 5V PSU board.?
Having recently read Hans’ excellent SMPS analysis ( ) it got me wondering what could have caused the fault. I had been powering my QMX from a USB-C battery and this 12v cable (). I then remembered that USB-C PD adapters typically start with the output at 5V and then shortly afterwards increase the voltage to that negotiated by the device (in this case 12V). This would generate exactly the voltage pattern Hans has told us to AVOID. I took a trace of the voltage power-up sequence, and this is the result (no QMX’s were harmed in creating this trace).
Output power starts at 5V for 120ms before increasing to 12V, perfectly creating Hans’ disaster scenario and causing D108 to sacrifice itself to protect the rest of the QMX. Thankfully the rest of my QMX appears to have survived unharmed, thanks to D108.
Conclusion: don’t use a USB-C battery to power your QMX, unless you’ve confirmed your adapter behaves differently!
